Disable ccache when use mingw.

Change-Id: Ieff363f9c4433bba53d1e94a25477c60933666e2
diff --git a/build/tools/windows_sdk.mk b/build/tools/windows_sdk.mk
index f02822f..ea8e4d7 100644
--- a/build/tools/windows_sdk.mk
+++ b/build/tools/windows_sdk.mk
@@ -60,7 +60,7 @@
 
 winsdk-tools: acp
 	$(call winsdk-banner,Build Windows Tools)
-	$(hide) USE_MINGW=1 $(MAKE) PRODUCT-$(TARGET_PRODUCT)-$(strip $(WIN_TARGETS))
+	$(hide) USE_MINGW=1 USE_CCACHE="" $(MAKE) PRODUCT-$(TARGET_PRODUCT)-$(strip $(WIN_TARGETS))
 
 $(WIN_SDK_ZIP): winsdk-tools sdk
 	$(call winsdk-banner,Build $(WIN_SDK_NAME))